Heat transfer fluids

ABSTRACT

An improved method for exchanging heat with an organic heat transfer fluid is disclosed. An effective amount of an alkaline earth metal overbased alkaline earth metal sulfonate having a base ratio of at least 4 is incorporated into the heat transfer fluid to reduce exchanger fouling.

United States Patent 1191 King et al. 5] Nov. 18, 1975 HEAT TRANSFER FLUIDS 2,695,273 11/1954 Hook et a]. 252/334 Inventors: J M- g, San Rafael; Robert 3,554,914 l/197l Nagy 252/75 L. Peeler Albany both of Calif Priniary Emmi Benjamin R Padgett ner- Assignee: Chevrpn Research p y San Assistant Exam'in'erDeborah L. Kyle I Franclsco, Cahf- Attorney, Agent, or Firm-G. F. Magdeburger; C. J. 22 Filed: Apr. 18, 1973 Tonkm 21 A l. N 352,152 PP 0 57] ABSTRACT An improved method for exchanging heat with an or- 2 252/75 208/48 ganic heat transfer fluid is disclosed. An effective I v amount of an alkaline earth metal overbased alkaline [58] Field of Search 252/75 208/48 AA earth metal sulfonate having a base ratio of at least 4 [56] References Cited is incorporated into the heat transfer fluid to reduce UNITED STATES PATENTS fouhng' 2,616,911 11/1952 Assef et al 252/334 9 Claims, N0 Drawings HEAT TRANSFER FLUIDS BACKGROUND OF THE INVENTION The use of heat transfer fluids is an essential part of many manufacturing operations. Typical operations include petroleum refining, chemical synthesis, asphaltic aggregate production, plywood lamination, plastic molding, etc. To permit operation at design capacity and to reduce heater hot spots, the heat transfer fluid should not cause serious fouling of the heat transfer surfaces.

Many organic heat transfer oils have been developed and have effected good heat transfer at elevated temperatures, typically 300 to 600F. The most common and most economical of these organic oils is the petroleum hydrocarbon oil, although, synthetic and chlorinated hydrocarbon oils are often used.

The use of an organic heat transfer oil in the high temperature applications has not been without problems. For example, during the operation of the exchanger, the organic medium comes into contact with the hot surfaces of the exchangers tubes. At these high temperatures the organic medium partially decomposes to form small amounts of gums and carbonaceous materials. The decomposition products form deposits and films on the surfaces of the exchanger tubes causing a significant reduction in the heat transfer coefficient. Continued operation under these conditions over prolonged periods reduces the heat transfer efficiency to such an extent that disassembly of the exchanger for extensive cleaning is typically necessary.

Numerous attempts have been made to ameliorate exchanger fouling. It has been proposed, for example, to use more stable aromatic hydrocarbon oils or to alleviate the fouling problem by incorporating antioxidants, dispersants, etc., into the transfer medium. These solutions have met with only limited success and have in some instances substantially increased the cost of the transfer medium.

In one method disclosed in US. Pat. No. 3,554,914, it is suggested that a calcium sulfonate be incorporated into the heat transfer oil. It was found that the presence of a calcium sulfonate having a base number between about 15 and 30 mg. KOI-I/g significantly reduced the heat exchange fouling.

Even though the use of the suggested calcium sulfonate reduces the degradation of the transfer medium,

heat exchanger fouling still remains a burdensome problem. A need therefore exists for a method for reducing heat exchanger fouling that is easy to perform and that is relatively inexpensive.

SUMMARY OF THE INVENTION We have found that heat exchanger fouling from an organic heat transfer medium can be substantially reduced by incorporating into the medium from 0.05 to 3 weight percent of an overbased alkaline earth metal aromatic sulfonate or mixtures thereof having a base ratio of at least 4.0.

Those alkaline earth metal sulfonates having a base ratio below 4.0 and particularly below 3.5 must be used at too high a concentration in order to sufficiently suppress exchanger fouling and, therefore, are not considered within the scope of this invention.

DETAILED DESCRIPTION OF THE INVENTION The fouling tendencies of an organic heat transfer medium can be significantly reduced by incorporating into the medium from 0.05 to 3 and preferably from 0.1 to 2 weight percent of an overbased alkaline earth metal aromatic sulfonate having a base ratio in excess of 4.0 and preferably between about 4.5 and 11 and more preferably from 5 to 10. The sulfonate portion should have a molecular weight between about 300 and 650 and preferably between about 500 and 550. Overbased materials are characterized by a metal content in excess of that stoichiometrically required by the reaction of the metal with the particular sulfonic acid. The base ratio is the ratio of the chemical equivalents of excess metal in the product to the chemical equivalents of the metal required to neutralize the sulfonic acid. Alkaline Earth Metal Sulfonates The neutral metal sulfonates which may be overbased to form the compounds useful in the practice of this invention can comprise any oil-soluble alkaline earth metal sulfonate. Preferably, these sulfonates have the following generalized chemical formula:

wherein:

M is an alkaline earth metal selected from magnesium, calcium, strontium, and barium, preferably calcium and barium or mixtures thereof;

R is hydrogen or an alkyl having from 10 to 22 carbons (preferably from 15 to 21) and preferably attached to the benzene ring through a secondary carbon atom; and

R is an alkyl having from 3 to 10 carbons when R is an alkyl and having from 8 to 22 carbons-when R is hydrogen.

In a preferred embodiment the neutral alkaline earth metal aromatic sulfonate is a dialkylbenzene sulfonate of the above formula wherein R is a straight chain aliphatic hydrocarbon radical of 17 to 21 carbon atoms, usually having at least 2 homologs present, and having secondary carbon attachment to the benzene ring and R is a branched chain alkyl group of 3 to 10 carbon atoms, more usually from 4 to 9 carbon atoms, having at least 1 homolog present, and preferably having at least two homologs present, and there being at least 1 branch of 1 to 2 carbon atoms, more usually of 1 carbon atom, i.e., methyl, per 2 carbon atoms along the longest chain. The attachment of the shorter alkyl group will generally be secondary or tertiary. Particularly preferred compositions have R with an average of 5 to 8 carbon atoms.

Usually, the difference in average number of carbon atoms between the short and long chain alkyl groups will be at least 10 and more usually at least 12, and not more than 16.

The preferred dialkylbenzene sulfonates which find use in the practice of this invention will generally have small amounts of monoalkylbenzene sulfonate, wherein the alkyl group is of from 17 to 21 carbon atoms present within the admixture. Preferably, the amount of the monoalkylbenzene sulfonate will not exceed 30% and more preferably the monoalkylbenzene sulfonate will not exceed 20% by weight of the total sulfonate. Generally, it will be in the range of about to weight percent.

The positions of the alkyl group and the sulfonate on the benzene ring in relation to each other are not critical to this invention. Generally, most of the isomeric possibilities will be encountered with the particular isomers having the least steric hindrance being predominant. Also, there will ,be a broad spectrum of isomers based on the carbon of the alkyl group bonded to the benzene ring, depending on the method of preparation and the reactants used in the preparation.

Illustrative short chain alkyl groups are isopropyl, tert.-butyl, neopentyl, diisobutyl, dipropenyl, tripropenyl, etc.

Illustrative of the long chain alkyl groups are heptadecyl, octadecyl, nonadecyl, eicosyl and heneicosyl.

Illustrative individual compositions are calcium isopropyleicosylbenzene sulfonate, barium tert.-butylnonadecylbenzene sulfonate, calcium dipropenyloctadecylbenzene, calcium diisobutyloctadecylbenzene sulfonate barium (propylene trimer) nonadecylbenzene sulfonate, etc.

The total number of carbon atoms in the alkyl groups will generally be in the range of at least about 20 and less than about 28. While small amounts of the dialkylbenzenes may be outside this range, the average number of carbon atoms of the alkyl groups over the total composition will be within the range.

In a preferred embodiment, a monoalkyl polypropyl benzene fraction having a boiling point range of about 318-478F. (ASTM D 447) containing from 4 to 9 carbon atoms (an average of 6 carbon atoms) and an average molecular weight of about 167 is alkylated with a substantially straight chain C,-,C cracked wax a-olefin. The molecular weight of the dialkylbenzene mixture has anaverage value in the range of 400-410.

The average molecular weights of the dialkylbenzenes used to prepare the sulfonate will generally be in the range of about 350 to 460, more usually in the range of about 375 to 425. I

The monoalkyl benzenes can be prepared by simply reacting benzene with 'a mono-olefin in a simple alkylation process. Typical alkylation catalysts include Friedel-Crafts catalysts such as hydrogen fluoride, aluminum chloride, phosphoric acid, etc. The alkylation temperatures will ordinarily be in the range of about 40 to 100F.

The preferred dialkyl benzenes can be prepared in substantially the same manner. A description of its preparation is disclosed in US. Pat. 3,470,097.

The dialkylbenzenes may then be readily sulfonated, using conventional sulfonation procedures and agents,

including oleum, chlorosulfonic acid, sulfur trioxide (complexed or thin film dilution techniques) and the like.

Various methods may be used to neutralize the sulfonic acid obtained, these methods being extensively described in the art. See for example US. Pat. Nos. 2,485,861 2,402,325 and 2,732,344.

The neutralization step is conveniently conducted by contacting the sulfonated alkyl or dialkyl benzenes with an aqueous sodium hydroxide solution. The product is a neutral sodium sulfonate. The neutral alkaline earth metal sulfonate is prepared by a simple metal exchange process. The sodium sulfonate is contacted with an alkaline earth metal salt, typically the halide salt, and the mixture heated. The exchange process is accomplished at temperatures of 50 to 150C and contact times of 0.5 to 10 hours, usually from I to 3 hours.

Ordinarily, the neutralized product will be mildly overbased, having from about 0.02 to 0.7 mol percent excess of basic alkaline earth metal over that required for neutralizing the acid values. Alkalinity values of these neutral compositions will generally be in the range of about 1 to 30, more usually from about 1 to 10 mg. KOI-I/g.

Overbasing of the Alkaline Earth Metal Sulfonate Various methods of overbasing calcium sulfonates to form superbased calcium compositions have been reported in the literature. See for example US. Pat. Nos. 2,695,910, 3,282,835 and 3,155,616, as well as Canadian Pat. 570,814. The preferred method employs a method similar to that described in US. Pat. No. 3,155,616.

The overbasing process can be conveniently conducted by charging to a suitable reaction zone the neutral alkaline earth metal sulfonate, an inert hydrocarbon solvent, an alkanol and an alkaline earth metal base. The mixture is agitated and maintained at a temperature and pressure sufficient to hold the alkanol within the liquid mixture. Carbon dioxide is then contacted with its reaction medium, preferably sparged or bubbled through the liquid mixture. The introduction of carbon dioxide is continued until its absorption rate into the mixture ceases or substantially subsides. Generally, from 0.2 to 1.6 mols and more usually from 0.9 to 1 mol of carbon dioxide will be absorbed by the mixture for every mol of alkaline earth metal base present. The metal base is preferably the alkaline earth metal oxides or hydroxides.

The crude reaction product is then heated to strip out the alkanol and water of reaction. The stripping will generally be conducted at temperatures below 150C and usually below C.

After the alkanol and water stripping has been terminated, the product may be filtered. In a preferred embodimenet, the hydrocarbon diluent is first stripped and then the product is filtered. Also, further addition of oil may be made to obtain a product having a somewhat lower alkalinity value and viscosity. The choice of the particular route will depend on the equipment, the materials used, their physical properties, and the product desired.

The stripping of the hydrocarbon diluent will generally be carried out at temperatures below 200C and will usually not exceed 175C, depending on the hydrocarbon diluents used. Preferably, when xylene is used, the temperature will not exceed C.

Occasionally, the final product will be filtered again to remove any adventitious particulate matter which may still be present.

The alkanol used, preferablymethanol, will generally have from about 0.1 to 1 weight percent water, more usually from about 0.3 to 0.7% water. The alkanol will generally be present in from aboutZ to 20, more usually from about 3 to 10 mol ratio to alkaline earth metal base. Usually, the total water present in the alkanol should be about 0 to 15 mol percent based on alkaline earth metal base, more usually 5 to 10 mol percent based on alkaline earth metal base.

The hydrocarbon diluent will be one having a boiling point higher than alkanol to permit its retention when the alcohol is removed during processing. The boiling point should generally be less than about 180C and 6 and terphenyls), polychlorinated biphenyls, alkyl biphenyl ethers, etc. Other Additives In addition to the overbased alkaline earth metal sulpreferably less than about 150C. Usually, the hydrofonate, other additives may be incorporated into the carbon diluent will form an azeotrope with water. The organic heat transfer medium without affecting its suusual diluents are aromatic hydrocarbons of from 7 to perior antifouling properties. A particulary advantacarbon atoms, having boiling points in the range of geous additive is an oxidation inhibitor. An exemplary about 100 to 180C. These include toluene, xylene, oxidation inhibitor is an alkaline earth metal amino cumene and cymene. The hydrocarbonaceous diluent 10 phenate prepared by reacting a Mannich base with an is present in an amount to form about a 5 to weight alkaline earth metal hydroxide or oxide. These compercent dispersion of alkaline earth metal base in the pounds are broadly described by the following generalinitial composition, usually an 8 to 15 weight percent ized structural formula:

0 %M O /2M 0 1AM CH, N-CH, 1

R R R wherein dispersion.

The amount of the sulfonate charged is based on the alkaline earth metal base charged: from about 6 to 50 equivalents of metal base will be used perequivalent of organic sulfonate, more usually from about 8 to equivalents of metal base per equivalent of organic sulfonate. Thus, alkalinity values can be achieved of 100 to 400 mg. KOH/g, preferably from about 150 to 380 mg.KOH/g.

Specific examples of exemplary alkaline earth metal sulfonates which may be employed in the practice of this invention or overbased to form the active component of this invention are disclosed in U.S. Pat. Nos. 3,691,075, 3,629,109, 3,595,790, and 3,537,996. These patents are herein incorporated by reference. Organic Heat Transfer Medium The organic heat transfer medium can comprise'any stable inert organic liquid having an initial boiling point of at least 600F and preferably above about 700F. A typical boiling range is from 750 to 900F.

The preferred and most widely used organic medium is hydrocarbon oilsand preferably those containing a high aromatic content. A discussion of various hydrocarbon oils is disclosed in U.S. Pat. No. 3,554,914 and includes heat transfer oils such as refined mineral oils, pale oils, bright sticjsm refined aromatic oils, bottoms from detergent alkylate, dimer alkylate bottoms, etc.

Particularly preferred hydrocarbon oils include neutral oils having a viscosity from 100 to 350 SUS at 100F and preferably from 150 to 250 SUS at 100F.

Exemplary commercial heat transfer oils include Chevron Heat Transfer Oils marketed by Chevron Oil Company, Mobiltherm 600, marketed by Mobil Oil Company, and Humbletherm 500 and Humbletherm N-500, marketed by EXXON Oil Company.

Other types of organic heat transfer oils include oils derived from coal products and synthetic oils, e.g., alkylene polymers (such as polypropylene, butylene, etc., and mixtures thereof), alkylene oxide polymers (such as polymers prepared by polmerizing alkylene oxide (ethylene oxide, propylene oxide) in the presence of water or alcohol, e.g., ethyl alcohol, carboxylic acid esters, alkylbenzenes, polyphenols (e.g., biphenyls M is an alkaline earth metal;

R is a straight-chain or branched chain saturated hydrocarbon radical having from 8 to 35 carbons;

R, is a lower alkyl having from 1 to 5 carbons; and

n is an integer generally varying from 0 to 25 and preferably at least 50 percent of the molecules having n varying from 3 to 25.

The molecular weight of the above composition varies over a wide scale, but 50 percent of the molecules should have a molecular weight above about 1,500.

Another antioxidant is 2,6-di-tert-butyl-p-cresol or 4,4-methylene bis(2,6-di-tert-butyl phenol).

The following examples are offered by way of illustration and not by way of limitation.

EXAMPLE 1 This example is presented to illustrate the preparation of a preferred dialkyl benzene sulfonate which is used to prepare the overbased metal sulfonates of this invention.

Benzene is alkylated using a tetramer polypropylene fraction and HF alkylation catalyst, a reaction temperature of about F, and efficient mixing. The hydrocarbon phase is separated, washed and fractionated. The lower alkyl fraction (boiling point range 318 to 478F, ASTM D 447 distillation) is collected as feed for the second'stage alkylation with a mixture of straight chain l-olefins. The average molecular weight of the above branched chain alkylbenzene is 164. This corresponds to an average of 6 carbon atoms per alkyl group in the mixture. The over-all alkyl carbon atom content corresponding to the above boiling point range is the C C range.

Using the above branched chain monoalkylbenzene and a substantially straight chain c -,C l-alkene fraction obtained from cracked wax, and hydrogen fluoride catalyst, the desired dialkylbenzene is produced in a stirred, continuous reactor. The l-alkene feed has the following characteristics:

Average mol weight 268 Average number of carbon atoms per alkyl group -continued Olefin distribution. weight percent:

C 2 C 22 C 39 C 32 C 5 Reaction conditions:

LHSV 2 Temperature, F 100 Monoalkylbenzene to a-olefin,

mol ratio 2-1 Hydrocarbon to HF ratio, volume 2.3-1

After reaction the settled product is separated into an organic phase and a lower HF acid phase. The crude dialkylbenzene organic phase is washed and then fractionated by distillation. A minor amount of forecut, mainly monoalkylbenzene, is collected up to an overhead temperature of about 450F at mm.Hg. The balance of the distillate is the desired product, and has an average molecular weight of abot 405. The difference between the average carbon atom content of the alkylchain types is about 13.

The dialkylbenzene prepared as in Example 1 is charged to a stirred reaction vessel fitted for temperature control along with 130 neutral oil which is substantially free of sulfonatable material. The volume ratio of the two materials is 3% to 4, respectively, and to this mixture is added, over a period of several hours, 2 volumes of 25% oleum. The reaction temperature is maintained at about 100F. Two phases developed in the settled mixture, the lower being a spent mineral acid phase and the upper being the desired sulfonic acid phase.

The separated sulfonic acid-oil mixture is then neutralized with one volume of 50% aqueous caustic diluted with volumes of aqueous 2-butanol. During the neutralization the temperature is maintained below about 1 10F, and after completion thereof the neutral solution is heated and maintained at 140F during a second phase separation. Two phases developed, a lower brine-alcohol solution and an upper neutral alcohol-sodium sulfonate solution.

EXAMPLE 2 The preparation of a neutral calcium sulfonate is illustrated in this example. A 3-liter glass flask is charged with 80 grams of calcium chloride and 800 milliliters of water. Thereafter, 1,500 grams of the sodium sulfonate as prepared by the method of Example 1 is charged to the flask. The contents are heated to 85F under agitation and maintained at these conditions for 1 hour. After one hour, the contents are allowed to phase separate and the water layer drawn off. 800 milliliters of distilled water is admixed with the sulfonate and heated for 1 hour. The phases are allowed to separate and the aqueous phase drawn off. The sulfonate is washed three additional times with water and one time with an aqueous isobutyl alcohol solution. The mixture is heated to 1 12C to remove any residual water arid isobutyl alcohol. 500 milliliters of toluene is added to the sulfonate and the admixture filtered through a Celite 512 filter. The product is stripped at 185C under 3 mm. Hg vacuum to yield 740 grams of neutral calcium sulfonate. Analysis of the product reveals 6.09 1.93 calcium -continued Base No.

EXAMPLE 3 Wt sulfated ash Wt metal Base No.

EXAMPLE 4 This example is presented to illustrate an exemplary overbasing procedure in preparing an exemplary overbased calcium sulfonate. A l-liter glass 3-necked flask is charged with 18.9 grams of calcium hydroxide, 20 milliliters of methanol, 250 milliliters of a petroleum aliphatic thinner (6% aromatic hydrocarbons, 250F initial BP and 310F end BP), and grams of a calcium sulfonate prepared by the method of Example 1 except containing 1.64 weight percent calcium. An additional 250 milliliters of the thinner is then added and the contents-stirred. Carbon dioxide is bubbled through the mixture at room temperature and stopped when the uptake rate leveled off. A total of 14 grams of CO is taken up by the mixture. The product is heated to C to remove methanol and water and thereafter the product is filtered through a Celite 512 filter. The thinner is stripped by heating to 180C at two mm.Hg vacuum. The yield of overbased metal sulfonate is 101 grams. The basic calcium content of the product is 7.71 wt with a base ratio of 5.8. The Base Number is measured to be 216 mg. KOH/g.

EXAMPLE 5 This example ispresented to illustrate an exemplary overbasing procedure in preparing an overbased barium sulfonate. A two-liter glass flask is charged with 50 grams of barium sulfonate as prepared by the method of Example 3, 500 milliliters of xylene, and 72 milliliters of methanol. Thereafter, 36.2 grams of barium oxide is added to the mixture in three separate drops each 10 minutes apart. Carbon dioxide is bubbled into the reaction mixture until a total of 12 grams are taken up. Methanol and water are removed by distillation and the product filtered through a Celite 512 filter. The xylene is stripped from the system by heating to 180C under a 2 mm.Hg. vacuum. The product has a barium base ratio of 4.7 and a base'riumber of mg.KOH/g.

EXAMPLE 6 properties of oils containing varying amounts and varying kinds of metal sulfonates.

In the test, the sample oil is placed in the test apparatus and heated to a temperature of 600 to 650F for a period of 240 to 504 hours. At the end of the test, the oil is visually observed for deposit content. The heavier the deposit, the greater the fouling tendencies of the heat transfer oil. The rating is:

HEAVY representing an opaque deposit MEDIUM representing a brown translucent deposit LIGHT representing a lacquer or slight staining of the test apparatus walls TRACE representing trace amounts of deposits with only partial coverage of the surface NONE representing no visual deposits.

The sample oils are prepared by incorporating varying amounts of a neutral or overbased metal sulfonate into a solvent refined Mid-continent 200 neutral oil. The neutral sulfonates are substantially prepared by the method of Examples 2 and 3. The overbased sulfonates are substantially prepared by the method of Examples 4 and 5.

The test apparatus comprises an elongated glass tube of 450 mm total length having l an upper tubular section open at its top, 100 mm in length, with a 16 mm tubing OD, (2) a middle section, 250 mm in length, with a 6 mm tubing OD and a lower section 100 mm in length with a 16 mm tubing OD and closed at its bottom end. The lower section is immersed in a salt bath which is maintained at a constant temperature of 600 or 650F. The upper section is equipped with a cooling jacket so that water may be circulated through the jacket to cool the sample oil within the tube. The sample oil is placed within the tube so that the oil in the lower section is heated to elevated temperatures from the salt bath and travels upward through the small diameter middle section to the upper section where it is cooled. Since the upper section is open to the atmosphere, the oil is in contact with air in this section.

The results from the various sample oils tested herein is displayed in the following Table I.

TABLE] 10 1 illustrates the heavy deposits associated with the test oil without the presence of an antifouling additive. Tests 2 and 12 illustrate the relatively little effect of neutral calcium and barium sulfonates on the fouling properties both exhibiting heavy deposits. Tests 3-1 1 and 14-19 illustrate the substantial reduction of deposit formation by using an overbased calcium or barium sulfonate having a base ratio above 4. Tests 2, 12, 13 and 20 illustrate the problems of using neutral or overbased metal sulfonates having a base ratio below 4. Tests 21 and 22 are presented to illustrate that variations in the data occur with this test apparatus. Thus, the data as a whole must be viewed in order to observe the effect of the various additives.

EXAMPLE 7 This example is presented to illustrate the preparation and effect of mixed overbased metal sulfonates. A l-liter 3-neck round-bottomed glass flask is charged with grams of a neutral calcium sulfonate is prepared by the method of Example 2, 500 ml of xylene and ml of methanol. While stirring the mixture, barium' oxide is added in three separate drops, each being 10 minutes apart. Carbon dioxide is bubbled through the mixture until 18 grams have been absorbed. The reaction medium is heated to 135C to distill out the methanol and water filtered through a Celite 512 filter and stripped of xylene by heating to C under a 2 mm. Hg. vaccum. The overbased barium/calcium sulfonate has a base ratio of 5.1 and contains 1.14 wt calcium and 19.8 wt barium. The product had a base number of 162 mg. KOH/g.

The above overbased barium/calcium sulfonate is tested in accordance with the procedure set forth in Example 6 and found to have the following effect on the heating oil:

Base Ratio 5.1

Concentration 0.51 mM./kg.

Temperature 600F Time 504 hours Heat Transfer Fouling Test Test Time Metal Sulfonate Additive Test Temp. Fouling Deposit Test Type Base Ratio Conc (1) (hrs) Amount 1 None 600 240 HEAVY 2 Neutral Calcium Sulfonate 0 7 600 240 HEAVY 3 Overbased Calcium Sulfonate 10.2 14 600 504 NONE 4 5.7 14 600 504 NONE 5 .5.7 21 600 S04 NONE 6 5.7 7 600 504 NONE 7 5.8 14 600 504 NONE 8 5.8 29 600 504 NONE 9 7.8 29 650 336 TRACE l0 10.2 29 650 336 TRACE ll 10.2 48 650 336 TRACE l2 Neutral Barium Sulfonate 0 14 600 240 HEAVY 13 Overbased Barium Sulfonate 0.6 7 600 240 MEDIUM 14 4.7 7 600 504 NONE 15 4.7 14 600 504 NONE 16 7.3 14 600 504 TRACE 17 5 .0 7 600 504 NONE 18 5.0 14 600 504 NONE l9 4.5 7 600 504 TRACE 20 Overbased Calcium Sulfonate 3.85 21 650 336 HEAVY 21 5.8 15 650 326 HEAVY 22 Overbased Barium Sulfonate 10.4 14 600 504 LlGHT MEDIUM "'As defined on page 3 "'Concentration of metal sulfonate in oil as expressed in mMJkg The above table illustrates the practice of the instant invention in reducing fouling of a heat transfer oil. Test Deposit Rating None We claim:

1. In a method of exchanging heat wherein an organic hydrocarbon heat transfer fluid boiling within the range of about 600 and 900F. is passed through one side of a heat exchanger and a process stream is passed through the other side to effect an exchange of heat between said heat transfer fluid and said process stream, an improvement for reducing the fouling properties of said heat transfer fluid comprising incorporating from 0.5 to 3 wt. percent of an oilsoluble alkaline earth metal carbonate overbased alkaline earth metal sulfonate into said heat transfer fluid, said alkaline earth metal sulfonate having a metal based ratio of at least 4, said alkaline earth metal sulfonate having the formula:

wherein M is an alkaline earth metal R is hydrogen or a C -C alkyl, and

R is an alkyl having from 3 to 10 carbons when R is an alkyl or an alkyl having 8 to 22 carbons when R is hydrogen.

2. The method defined in claim 1 wherein said metal base ratio is between about 5 and 10.

3. The method defined in claim 1 wherein said alkaline earth metal carbonate overbased alkaline earth metal sulfonate is calcium carbonate overbased calcium sulfonate.

4. The method defined in claim 1 wherein said alkaline earth metal carbonate overbased alkaline earth metal sulfonate is baium carbonate overbased barium sulfonate.

5. The method defined in claim 1 wherein said alkaline earth metal carbonate overbased alkaline earth metal sulfonate is barium carbonate overbased calcium sulfonate.

6. The method defined in claim 1 wherein said alkaline earth metal carbonate overbased alkaline earth metal sulfonate is calcium carbonate overbased barium sulfonate.

7. The method defined in claim 1 wherein said alkaline earth metal carbonate overbased alkaline earth metal sulfonate is present in said heat transfer fl'uid in an amount from 0.l to 2 weight percent.

8. The method defined in claim 1 wherein said hydrocarbon is highly aromatic.

9. The method defined in claim S-Wherein an oxidation inhibitor is also incorporated into said heat transfer fluid. 

1. IN A METHOD OF EXCHANGING HEAT WHEREIN AN ORGANIC HYDROCARBON HEAT TRANSFER FLUID BOILING WITHIN THE RANGE OF ABOUT 600*F. AND 900*F. IS PASSED THROUGH ONE SIDE OF A HEAT EXMIXTURE OF MONO- OR POLYUREA COMPOUNDS HAVNG AN AVERAGE FROM 1 TO 8 UREDIO GROUPS AND HAVING A NUMBER AVERAGE MOAND SAID PROCESS STREAM. AN IMPROVEMENT FOR REDUCING THE BOILING PROPERTIES OF SAID HEAT TRANSFER FLUID COMPRISING INCORPORATING FROM 0.5 TO 3 WT. PERCENT OF AN OILSOLUBLE ALKALINE EARTH METAL CARBONATE OVERBASED ALKALINE EARTH METAL SULFONATE INTO SAID HEAT TRANSFER FLUID, SAID ALKALINE EARTH METAL SULFONATE HAVING A METAL BASED RATIO OF AT LEAST 4, SAID ALKALINE EARTH METAL SULFONATE HAVNG THE FORMULA:
 2. The method defined in claim 1 wherein said metal base ratio is between about 5 and
 10. 3. The method defined in claim 1 wherein said alkaline earth metal carbonate overbased alkaline earth metal sulfonate is calcium carbonate overbased calcium sulfonate.
 4. The method defined in claim 1 wherein said alkaline earth metal carbonate overbased alkaline earth metal sulfonate is baium carbonate overbased barium sulfonate.
 5. The method defined in claim 1 wherein said alkaline earth metal carbonate overbased alkaline earth metal sulfonate is barium carbonate overbased calcium sulfonate.
 6. The method defined in claim 1 wherein said alkaline earth metal carbonate overbased alkaline earth metal sulfonate is calcium carbonate overbased barium sulfonate.
 7. The method defined in claim 1 wherein said alkaline earth metal carbonate overbased alkaline earth metal sulfonate is present in said heat transfer fluid in an amount from 0.1 to 2 weight percent.
 8. The method defined in claim 1 wherein said hydrocarbon is highly aromatic.
 9. The method defined in claim 8 wherein an oxidation inhibitor is also incorporated into said heat transfer fluid. 